Why has this guy suddenly changed? From acting like he likes me to not?

Me and this guy liked eachother since around May and we'd acted like a couple b4 but only a few times but throughout summer this guy said he liked me to my friend and he slept round mine (nothing sexual) just cuddling and hugs and kisses and we got drunk for fun as exams were over and went out to places and just we clicked so much but as soon as we go back to last year of school he's just so shy:/ he'll hover around me but won't say anything he'll stand next to me but won't say a word. He'll only talk to me if I'm part of a convo and he'll be like "I know right aha" but never a one to one. I don't get it as he was so outgoing in summer we just messaged all the time he used to message me first and hug me and all this cute stuff but now back in school he's just so different and he doesn't message me anymore. My friend said he always looks at me but I don't even know. I hope this means he hasn't lost interest I really haven't done anything for him to have lost it :(